Since you have the powder, try dropping to 70 grains of powder first. Then try some 240 & 300 grain Hornady XTP's. The T/C mag express XTP's will work great and they come with their own sabot. If the 70 grains is working good then move it to 75 and so on. Then again, it might be a rifle that just does not like Triple Se7en and wants something a little slower burning. My Wolverine also shoot Shockwaves very well.

I talk to a person all the time with the same rifle you have. He shoots 80 grains of Goex 2f and a 240 grain XTP out of his Bighorn. As for power, he has blown through every deer he has shot with it in Kansas and Pennsylvania so he can not tell you how the bullets look after being shot. He does report excellent accuracy like my Wolverine does, and the deer drop dead. Which is the main thing.

The Knight & Noslerbullets should have shot well... are you swabbing the barrel between shots? Also what are you using for a swab solution? Any rifle that shoots a #11 cap, I swab 9 out of 10 times with pure isopropyl alcohol. A lightly damp patch and then two dry ones. While #11 will fire loose powder well, it does not take to swabbing as well as the 209 primers do.

Something you might want to try just for kicks.. next time at the range, load 90-100 grains of Triple Se7en 2f and that Nosler and see how the rifle shoots. You might have one of them powder junkie rifles. My Knight Disc is one of them. I must have shot four pounds of powder through that thing trying to find the sweet load. Finally one day on the range I was shooting my T/C Black Diamond XR and my Knight. I had the powder measure set for 110 grains of powder. When it came time to shoot the Knight I did not change the charge back.. Well low and behold, the projectiles (300 grain Shockwaves) were cutting each other at 50 yards... It was a powder junkie rifle. As long as I keep the charge over 100 grains that rifle will shoot. Although it does have a 24" barrel.